Re: [Tinycc-devel] precompiled headers

[Michael Matz]

Hi,

On Sun, 24 Apr 2016, Sergey Korshunoff wrote:

> As I see this today. For example, I prefer to speed up tccboot kernel
> compilation.
> A current command to compile is like
>  tcc -o vmlinux linux/kernel/init.c linux/arch/kernel/head.c ...
>
> With -cheaders[=dDIR] option tcc will precompile headers in each *.c
> before  the first C token is seen and create files
> [DIR]linux/kernel/init.tch, [DIR]linux/arch/kernel/head.tch,...  or
> use these files if they already present. I think this is better and
> don't need a special tuning.

This cmdline interface seems sensible.  I must warn you, though, that 
precompiled headers aren't totally trivial to get right.  Depending on for 
you go with precompilation.  If you save the tokens before 
macro-expansion is the easiest.  If you save them after expansion you have 
to take care of including headers in different environments. E.g. in these 
two files:

% cat a.c
#define FOO
#include "header.h"
% cat b.c
#define BAR
#include "header.h"

the include file header.h might expand to a different token sequence 
depening on if FOO or BAR are defined.  Such define can also be hidden in 
headers included before header.h.  If you go even further and don't just 
store token sequences but code snippets the complications will only 
increase.  Just something to keep in mind in the implementation.


Ciao,
Michael.